The broad, long-term objective of this proposal is the better understanding of the forces and interactions that underlie protein structure and folding. The specific aims are: 1) To measure the equilibrium constant for loop formation in a diverse series of synthetic peptides incorporating omega loop sequences, and to relate functional properties and primary structure to the tendency for loop closure. 2) To determine whether loop peptides take on stable structure in aqueous environments. 3) To characterize the structure(s) of selected loop peptides by NMR and other spectroscopic methods. 4) To describe the context dependence of loop formation by synthesizing peptides containing loop sequences plus N- and C-terminal extensions derived from the protein sequence, or from known helical "caps". 5) To determine sequence requirements for loop formation and stabilization. 6) To develop a means for predicting the occurrence and conformation of omega loops in proteins of unknown structure. 7) To design, construct, and characterize an independently stable omega loop. The relationship of this project to health-related issues is that further information concerning protein structure and folding is essential for developing new pharmaceuticals based on drug-protein interactions, and for designing and producing natural, modified, or totally new proteins for therapeutic purposes. The experimental strategy is to use synthetic peptides containing omega loop sequences to address questions regarding loop structures and their relationship to protein structure and folding. The methods to be used are 1) a thiol-disulfide assay for loop closure quantitated by HPLC, 2) 1D and 2D NMR methods to assay for non-random conformation, and gather high- resolution structural data, 3) fluorescence and circular dichroism spectroscopy for structural assays, and 4) distance geometry computations to determine peptide structures from NMR data.